13G 



Messrs. S. G. Shattock and L. S. Dudgeon. [Feb. 20, 



As a comparable test of the action of sunlight upon B. pyocyaneus in the 

 moist state, an agar slant from which the water of expression had gone, was 

 inoculated, without disturbing the surface, with a 24 hours' growth of the 

 bacillus in peptone water. The end of the tube was sealed in the blowpipe flame, 

 and the tube was exposed on July 20, in the same dish of water as used on 

 that day for certain of the observations already recorded, for four hours' 

 sunshine (interrupted). The end of the tube was then removed, and the agar 

 medium covered by pouring in litmus glucose broth ; the tube was thereupon 

 plugged with sterilised wool. 



A growth of the bacillus (identified by sub-culture) followed in this case as 

 in that of the dried film exposed for the same time on the same day. 



A second control made in precisely the same way upon an agar slant, from 

 a 24 hours' growth in peptone water, and exposed on July 21 for five and 

 a-half hours' uninterrupted sunshine (from 11.30 A.M. to 5 p.m.), proved sterile, 

 like the dried slip from the vacuum tube exposed to uninterrupted sunlight 

 for six hours. 



It is thus abundantly clear that bright sunlight is lethal within six hours 

 to B. pyocyaneus in the dried state, in vacuo, and that the resistance of the 

 dried bacillus to this agency is not materially exalted, if it is increased at all, 

 under the condition last stated. 



The results show, in passing, that the view sometimes taken of the lethal 

 effect of sunlight upon bacterial cultures, viz., that it is due to chemical 

 decomposition of the medium on or in which the micro-organism is growing, 

 is unnecessary to explain the result. 



This being so, it was, perhaps, hardly necessary to test the lethal action of 

 the short wave-lengthed ultra-violet rays upon the dried bacillus, except for 

 the sake of confirming an obvious deduction by actual demonstration. 



In the following experiment, the action of the ultra-violet rays was tested 

 upon B. pyocyaneus, which had been dried in vacuo, but upon the slip after 

 its removal from the vacuum tube, and in an atmosphere of nitrogen. 



It may be noted here that the intense light generated by the apparatus is 

 per se also lethal, but not within the same time. This admits of being 

 demonstrated by intercepting the passage of the ultra-violet rays by means 

 of mica. 



May 26, 1911— A set of slips were inoculated with a 24 hours' growth of 

 B. pyocyaneus in peptone water. A slip was transferred to each of four 

 tubes, which were then exhausted, etc., and kept for five days, connected 

 with the bulb of charcoal surrounded with liquid air. 



May 31. — One of the tubes was opened, and the slip removed and exposed 

 in an atmosphere of nitrogen for 15 minutes to the action of the ultra-violet 



